SAN FRANCISCO -- Cyprus Tohono Corporation, a former Phelps Dodge subsidiary, has agreed to fund an estimated $6 million groundwater investigation at the Cyprus Tohono Mine Site, a copper mine southwest of Casa Grande, Ariz.

The agreement requires Cyprus to thoroughly investigate the groundwater and pay future oversight costs incurred by the EPA.

“This investigation of uranium-contaminated groundwater will guide the EPA in selecting and designing a cleanup remedy that is effective at protecting human health and the environment,” said Keith Takata, the EPA’s Superfund director for the Pacific Southwest region.

Currently, Cyprus, in consultation with the Tohono O’odham Nation and the EPA, is voluntarily investigating uranium-contaminated groundwater at the site. The EPA, Tohono O’odham and Cyprus will meet with Cypus to formalize the groundwater investigation on October 20. Under EPA oversight, Cypress recently completed a $49 million cleanup, where approximately 4.4 million cubic yards of mine waste of all affected areas was placed into a lined repository with soil cover and revegetation. Seeding and vegetation growth monitoring will continue over the next three years.

The 10,505-acre copper mine is located 32 miles south of Casa Grande on the Tohono O’odham Nation near North Komelik. Mining operations on the property have occurred sporadically since the 1880s, but large-scale open-pit mining of copper oxide ore began in the 1950s, and underground mining began in 1970.